Decade-long impact factors in ophthalmology journals and the effect of journal characteristics: a longitudinal study

Abstract

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The quality of published literature is evaluated by various metrics, wherein an important one is an impact factor (IF) available in Journal Citation Report (JCR). The IF range varies across fields of science^(1)^. Bibliometric trends and citation analysis in ophthalmology have been reported for 1997-2013^(2-4)^. Vainer et al. attributed an increase in IFs of ophthalmology journals to an annual increase in the number of ophthalmology journals^(1)^. Since the explosion of open access journals, there is a lack of literature on the recent trends in IFs for ophthalmology journals. Herein, we evaluated and reported the trends in IFs of ophthalmology journals over the last decade.

The data on IFs were collected from the JCRs released annually by Thomson Reuters (2009-2015) and Clarivate Analytics (2016-2020). Other information related to journals, such as geographical origin, age, publication frequency, type of content (general/special), and nature of access (open access/not), was collected from the journals’ online webpages. The geographical regions of origin were grouped under America, Europe, and Australasia. America included Brazil, Canada, and United States; Europe included Austria, Denmark, England, France, Germany, Netherlands, and Switzerland; and Australasia included Australia, mainland China, India, Iran, and Japan.

Sixty-seven ophthalmology journals had IF in the 11- year period (2009-2019). The number ranged from 46 (2009) to 60 (2019) with a median of 59 (interquartile range (IQR), 57-60), and there was no statistically significant increase during this period (p=0.07), whereas the median (1.749-1.976, 0.048/year, p=0.004, R^2^=0.63), minimum (0.510-0.605, 0.051/year, p=0.02, R^2^=0.50), and maximum (7.755-14.860, 0.469/year, p=0.003, R^2^=0.65) IFs increased significantly. Mean IF was 1.716, 1.747, 1.791, 1.733, 1.960, 1.997, 2.002, 2.208, 2.325, 2.394, and 2.510 for the years 2009-2019, respectively. The number showed a significant increase from 41 in 2000 to 58 in 2013, and the maximum IF significantly increased from 4.682 to 9.897^(1)^.

Approximately 70% had a publication scope in the areas of general ophthalmology and optometry, whereas ~30% were specialty journals focusing on specific topics, such as cataract, contact lens, cornea, eye movement, glaucoma, neuro-ophthalmology, ocular surface, ophthalmic plastic surgery, paediatric ophthalmology, refractive surgery, retina, vision electrophysiology, and visual neuroscience. The median age was 38 years (IQR, 25-166 years). American journals constituted 56.7%, whereas European and Australasian journals comprised 32.8% and 10.5%, respectively. Approximately 14.9% were open access journals. Median publication frequency was six issues/year (IQR, 6-12 issues/year). There was no effect of age (p=0.66), geographical origin (p=0.16), publication frequency (p=0.28), content type (p=0.49), and access nature (p=0.07) on longitudinal trends in IFs.

For the IF analyses as a function of time (year), journals that had at least IFs for a minimum of ten years (n=52) were considered, and their names were deidentified. Among these, 27 journals (51.9%) showed statistically significant increasing trends in IF (Table 1), whereas 24 (46.2%) showed no trend. Only one journal had a significant decrease in IF. Comparing journals with an increasing trend in IF and those without trend, there were no significant differences in journal age, geographical origin, publication frequency, content type, and access nature (Table 2). It may be a general nonspecific trend not limited to ophthalmology and can be explored in other fields.

Mansour et al. categorized the top 19 journals in ophthalmology and reported that subspecialty journals had lower IFs than general ophthalmology journals^(3)^, although it may not be appropriate to compare IFs based on content in different areas. Although subspecialty journals had a higher self-citation rate than general ophthalmology journals, the self-citation rate does not affect IF in ophthalmology, unlike in other fields^(5)^. Further, open access has not affected the citation of ophthalmology articles. This can be explained by a higher number of articles published in ophthalmology by Western countries who have subscribed access through either institution or library^(6)^.

Other possible factors that are not evaluated in our study include the number of articles published/year, availability of advance online publication, tweetations, publication time lag, content type, study nature, article length, and numbers of citations, references, and authors. Publication time lag typically does not affect the IFs of ophthalmology journals^(7)^. It was reported that bias in the positive and negative results exists in ophthalmic literature, and positive results were published in journals with higher IF^(8)^.

Although there are advantages in considering IF to analyze research content, there are also limitations. Different fields have varied IFs; for example, in 2019, the topmost journals in oncology and ophthalmology had IFs of 292.278 and 14.860, respectively. There is a varied disparity in IF across disciplines. Sometimes, even negative citations are counted for calculating IF, which means that both positive and negative citations were equally treated in the assessment^(3)^. Further, some journals are hybrid in nature that can carry variable proportions of open and closed access papers.

A 2-year IF is still a standard. IFs can be higher in longer citation windows. Some articles, known as sleeping beauties^(9)^, were recognized much later after publication. Analysis of 28 ophthalmologic journals revealed that IFs of 3- and 4-year citation windows were appropriate to analyze research quality^(10)^.

Impact factors can seriously affect editorial policies, such as accepting a greater number of review articles, coercive citation, i.e., editors forcing authors to add a spurious citation, and omission of relatively less citable items, such as a letter to editors, photo-essays, and case reports. One of the current top 15 ophthalmology journals had the highest relative increase in IF, which correlated with a decrease in the number of articles published with time. A dramatic rise in IF of one of the current top 10 ophthalmology journals is reported, which was explained by online access, editorial policy changes, and revolutionary diagnostic and therapeutic advances in subspecialty research^(3)^.

To our knowledge, this is the first study to evaluate impact factors in ophthalmology journals over the last decade and the only study that categorized journals based on their trends and evaluated various factors influencing IFs. Future studies can evaluate other factors and trends in IF during the post-COVID era and compare them with our results to understand the growth of ophthalmic literature.